Ruthenium red-mediated osmium binding for examining uncoated biological material under the scanning electron microscope.

A simple technique for examining uncoated soft biological material under the scanning electron microscope is described. Rat tissues were initially fixed in 2.5% glutaraldehyde either by intravascular perfusion or by immersion. The samples were placed in buffered 2.5% glutaraldehyde containing 0.05% ruthenium red and postfixed in buffered 1% osmium tetroxide containing 0.05% ruthenium red. The samples were alternately incubated 3 to 5 times in 1% OsO4 and 0.1% ruthenium red solutions with continuous shaking at room temperature. The specimens were dehydrated, critical point dried, mounted and examined under the scanning electron microscope. Contour details were clearly defined at both the external and cut surfaces of the tissues. The specimens could be observed for more than 30 minutes without excessive charging or glow effects and the material remained stable under the beam at 20-25 kV and at various magnifications.